The segment of I-10 in California, also known as the Pearl Harbor Memorial Highway,[4] runs east from Santa Monica through Los Angeles, San Bernardino, and Palm Springs before crossing into the state of Arizona.

[6] However, the California State Legislature removed this designation following the passage of a bill on August 31, 2022.

[15] The Santa Monica Freeway is I-10 from SR 1 to I-5, as named by the State Highway Commission on April 25, 1957.

[7][8] The Santa Monica Freeway is the westernmost segment of I-10, beginning at the east end of the McClure Tunnel in Santa Monica and ending southeast of Downtown Los Angeles at the East Los Angeles Interchange.

I-10 begins its eastward journey in the city of Santa Monica after SR 1 turns east through the McClure Tunnel.

I-10 then continues through Sawtelle, Rancho Park, Cheviot Hills, Beverlywood, and Crestview in West Los Angeles; Lafayette Square and Wellington Square in Mid City; and Arlington Heights, West Adams, and Jefferson Park into Downtown Los Angeles.

[23] In Riverside County, I-10 goes through Calimesa before entering Beaumont and merging with the eastern end of SR 60 (itself formerly the California segment of US 60).

Three miles (4.8 km) south of I-10 at the Wiley's Well exit, between Desert Center and Blythe, are the Chuckawalla Valley and Ironwood state prisons.

In Los Angeles County, the El Monte Busway is a grade-separated, shared-use HOT and express bus corridor running along the San Bernardino Freeway between Alameda Street near Union Station in Downtown Los Angeles and a point west of I-605 in El Monte.

From Alameda Street to I-710, the El Monte Busway runs parallel to the north side of the freeway.

In both segments, solo drivers are tolled using a congestion pricing system based on the real-time levels of traffic.

As of 2024[update], the proposed segment in Los Angeles County to bridge the gap between I-605 and the San Bernardino County line is under environmental review,[31] the section from Etiwanda Avenue to Pepper Avenue in Colton is planned to break ground in 2025, and the segment to Ford Street in Redlands is still in the planning stage.

[32] What is now I-10 east of Los Angeles was generally part of the Atlantic and Pacific Highway, one of many transcontinental national auto trails.

[33] In late 1926, US 99 was designated along the section of road from San Bernardino to Indio, where it turned south along present SR 86 on the west side of the Salton Sea.

LR 26 was extended west from San Bernardino to Los Angeles in 1931, running along an alignment south of the existing US 66/US 99.

A four-mile (6.4 km) section of today's freeway was built between 1933 and 1935 at a cost of $877,000 (equivalent to $15.3 million in 2023[37]).

The "Ramona Boulevard" highway linked downtown Los Angeles to the communities of the southern San Gabriel Valley.

The roadway, which opened on April 20, 1935, was dubbed the "Air Line route" and was seen as a major achievement in traffic design.

[citation needed] It was later replaced by the Santa Monica Freeway and added to the Interstate Highway System on September 15, 1955.

Portions of the Santa Monica Freeway going over La Cienega Boulevard collapsed after the Northridge earthquake on January 17, 1994, and were rebuilt using new seismic-resistant bridge designs.

[41] The El Monte Busway was converted to HOT lanes in 2013 as part of the Metro ExpressLanes project.

[42] On July 19, 2015, a bridge carrying the eastbound lanes of I-10 near Desert Center collapsed from floodwater from the remnants of Hurricane Dolores, trapping a vehicle.

[43][44] Shortly after midnight of November 11, 2023, a mile-long (1.6 km) segment of the freeway in Downtown Los Angeles between Alameda Street and Santa Fe Avenue suffered significant damage due to a fire at a pallet yard underneath the freeway.

[45][46] The Los Angeles Times reported a couple of days later that "sanitizer accumulated during the height of the COVID-19 pandemic was stored under the overpass and helped fuel the flames".

[47] Governor Gavin Newsom declared a state of emergency in response to the fire; the freeway was reopened after eight days, far ahead of the original five-week estimate.